Method of horizontally growing carbon nanotubes and field effect transistor using the carbon nanotubes grown by the method

ABSTRACT

Disclosed is a method of horizontally growing carbon nanotubes, in which the carbon nanotubes can be selectively grown in a horizontal direction at specific locations of a substrate having catalyst formed thereat, so that the method can be usefully utilized in fabricating nano-devices. The method includes the steps of: (a) forming a predetermined catalyst pattern on a first substrate; (b) forming a vertical growth preventing layer on the first substrate, which prevents carbon nanotubes from growing in a vertical direction; (c) forming apertures through the vertical growth preventing layer and the first substrate to expose the catalyst pattern through the apertures; and (d) synthesizing carbon nanotubes at exposed surfaces of the catalyst pattern in order to grow the carbon nanotubes in the horizontal direction.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method of growing carbonnanotubes, and more particularly to a method of horizontally growingcarbon nanotubes, in which the carbon nanotubes can be selectively grownin a horizontal direction at specific locations of a substrate havingcatalyst formed thereat, so that the method can be usefully utilized infabricating nano-devices.

[0003] Also, the present invention relates to a method of horizontallygrowing carbon nanotubes, in which catalysts are formed in a shape ofnanodots or nanowires at desired specific locations, so that the carbonnanotubes are selectively grown at specific locations, thereby themethod can be usefully utilized in fabricating nano-devices.

[0004] Furthermore, the present invention relates to a field effecttransistor, in which carbon nanotubes are grown in a horizontaldirection to form a carbon nanotube bridge achieving a field effecttransistor (FET), and in which catalysts in contact with a source and adrain, between which a carbon nanotube bridge is formed, are magnetizedin a desired direction, so as to simultaneously achieve both a spinvalve and a single electron transistor (SET).

[0005] 2. Description of the Related Art

[0006] A carbon nanotube has a construction of one-dimensional quantumwire and has good mechanical and chemical characteristics. Also, it hasbeen known that the carbon nanotube reveals very interesting electriccharacteristics such as the phenomenon of quantum transport. Furthersmuch of attention has been paid to the carbon nanotube as a newmaterial, since it has newly discovered special characteristics, inaddition to the above characteristics,

[0007] In order to utilize the superior characteristics of the material,a re-executable process of fabricating the carbon nanotube has to bepreceded. However, in the existing process, after the carbon nanotubesare fabricated, they are individually handled one by one to be locatedat a desired position. Therefore, it is difficult to apply the existingprocess, in which the grown carbon nanotubes are located at desiredpositions in “an individual handling mode”, to an electronic element ora highly-integrated element, and many researches and developments arenow being conducted in order to overcome this problem.

[0008] Further, in the vertical growth method, which is an existingmethod of synthesizing the carbon nanotubes, carbon nanotubes 6 aregrown in the vertical direction in a shape of a well-arranged barleyafield on a substrate 2, on which a pattern 4 of catalyst is formed.Regarding the vertical growth method, a large quantity of report alreadyexits.

[0009] However, in order to utilize the carbon nanotube as a nano-devicehaving a new function, a technique capable of selectively growing thecarbon nanotubes in the horizontal direction at specific positions ismore useful and more highly required than the vertical growth technique,in a viewpoint of appliance.

[0010] The first report, which illustrates that carbon nanotubes can behorizontally grown between patterned metals to be connected with eachother, was made by Hong Jie Die as shown in FIG. 2 (see Mature, vol.395, page 878) FIG. 2 is a view for schematically showing the method ofhorizontally growing carbon nanotubes reported by Hong Jie Die. However,FIG. 2 apparently shows that a great many carbon nanotubes are grown notonly in the horizontal direction but also in the vertical direction.This is because the carbon nanotubes are grown from surfaces of catalystmetal and moreover are randomly grown at all exposed surfaces of thecatalyst.

[0011] In addition, since an effect of giant magneto resistance (GMR)was discovered in a multi-layer film comprising magnetic metal and non-magnetic metal in 1988, a research about a magnetic metal thin film isbeing widely conducted around the world. Moreover, since electrons existin a spin-polarized state in the magnetic metal, polarized spin currentcan be generated by utilizing this characteristic. Therefore, a greateffort has been made to understand and to develop the spin electronics(spintronics) or the magneto electronics by utilizing the degree offreedom of spin which is an important inherent characteristic of theelectron.

[0012] Recently, such phenomena as tunneling magneto resistance (TMR)and giant magneto resistance (GMR) discovered in the magneticmulti-layer film system of nano-structure have already been applied in amagneto resistance (MR) magnetic head element and placed in a hard discdrive (HDD) of a computer to be commercialized.

[0013] In this case, TMR means a phenomenon, in which the tunnelingcurrent changes according to the relative magnetized direction of aferromagnetic material in a junction having a construction offerromagnet/dielectric (semiconductor)/ferromagnet, and which has alarger magnetic resistance ratio and a larger field sensitivity thanother magnetic resistance, so that a research for utilizing it in amaterial for magnetic random access memory (MRAM) or magnetic resistancehead of next generation has been actively performed. However, are-executable formation of dielectric layer and reduction of junctionresistance become serious problems.

[0014] Currently, a large number of scientists in the field of magneticapplication are actively conducting researches in manufacturing MRAMs,utilizing a magnetic tunneling junction (MTJ) and a spin valve showingthe phenomenon of magnetic resistance in the low magnetic field.

SUMMARY OF THE INVENTION

[0015] Accordingly, the present invention has been made in an effort tosolve the aforementioned problems, and it is an object of the presentinvention to provide a method of horizontally growing carbon nanotubes,in which the carbon nanotubes can be selectively grown in a horizontaldirection at specific locations of a substrate having catalyst formedthereat, so that the method can be usefully utilized in fabricatingnano-devices.

[0016] Still, it is another object of the present invention to provide amethod of horizontally growing carbon nanotubes, in which catalysts areformed in a shape of nanodots or nanowires at desired specificlocations, so that the carbon nanotubes are selectively grown atspecific locations, so that the method can be usefully utilized infabricating nano-devices.

[0017] Still, it is another object of the present invention to provide afield effect transistor, in which carbon nanotubes are grown in ahorizontal direction to form a carbon nanotube bridge, so as to achievea field effect transistor (FET), and in which catalysts in contact witha source and a drain, between which a carbon nanotube bridge is formed,are magnetized in a desired direction, so as to simultaneously achieveboth a spin valve and a single electron transistor (SET).

[0018] In accordance with one aspect, the present invention provides amethod of horizontally growing carbon nanotubes, the method comprisingthe steps of (a) forming a predetermined catalyst pattern on a firstsubstrate; (b) forming a vertical growth preventing layer on the firstsubstrate, which prevents carbon nanotubes from growing in a verticaldirection; (c) forming apertures through the vertical growth preventinglayer and the first substrate to expose the catalyst pattern through theapertures; and (d) synthesizing carbon nanotubes at exposed surfaces ofthe catalyst pattern, so as to grow the carbon nanotubes in thehorizontal direction.

[0019] In this case, the apertures formed in the step c are of ahole-type, in which the apertures extend entirely through the verticalgrowth preventing layer and the first substrate, or a well-type, inwhich the first substrate is partially etched, so that the aperturesextend through the vertical growth preventing layer and a portion of thefirst substrate.

[0020] In accordance with another aspect, the present invention providesa method of horizontally growing carbon nanotubes, the method comprisingthe steps of: (i) forming masks at predetermined locations on a firstsubstrate; (j) forming a catalyst pattern on the first substrate and themasks formed on the first substrate; (k) forming a vertical growthpreventing layer on the first substrate, which prevents the carbonnanotubes from growing in a vertical direction; (l) eliminating themasks from the vertical growth preventing layer and the first substrate,so as to form apertures and expose the catalyst pattern; and (m)synthesizing the carbon nanotubes at exposed locations of the catalystpattern, so as to grow the carbon nanotubes in the horizontal direction.

[0021] In accordance with another aspect, the present invention providesa method of horizontally growing carbon nanotubes, the method comprisingthe steps of: forming a catalyst pattern in a predeterminedtwo-dimensional arrangement on a first substrate; fabricating a secondsubstrate for preventing vertical growth of the carbon nanotubes havingholes in a predetermined arrangement; placing the second substrate forpreventing vertical growth of the carbon nanotubes over the firstsubstrate having the catalyst pattern with a predetermined gap; andsynthesizing the carbon nanotubes at the catalyst pattern, so as tohorizontally grow the carbon nanotubes.

[0022] In accordance with another aspect, the present invention alsoprovides a method of horizontally growing carbon nanotubes, the methodcomprising the steps of: forming a catalyst in a shape of nanodots ornanowires on a substrate; patterning a growth preventing layer on thecatalyst in the shape of nanodots or nanowires, so as to prevent thenanodots or nanowires from growing in a vertical direction; andselectively growing the carbon nanotubes in a horizontal direction atthe nanodots or nanowires.

[0023] In this case, the catalyst in the shape of the nanodots ornanowires are patterned by an imprint method or a self-assembly method.

[0024] Further, the growth preventing layer may be formed of aninsulator film lade from a compound selected from the group consistingof silicon nitride (SiN) and silicon oxide (SiO₂), or may be formed froma metal selected from the group consisting of Palladium (Pd) Niobium(Nb), and Molybdenum (Mo).

[0025] In accordance with another aspect, the present invention alsoprovides a method of horizontally growing carbon nanotubes, the methodcomprising the steps of: forming catalysts in a shape of nanowires on asubstrate; forming a growth preventing layer on the catalysts having theshape of nanowires by a semiconductor process including a lithographyprocess, the growth preventing layer being spaced from the substratewith a predetermined gap; eliminating a portion of the catalysts havingthe shape of nanowires in an area at which the growth preventing layeris not formed, by means of a wet etching; and growing the carbonnanotubes in a horizontal direction between the catalysts formed underthe growth preventing layer spaced from the substrate with apredetermined gap, by means of a chemical vapor deposition method.

[0026] Furthermore, in accordance with another aspect, the presentinvention also provides a field effect transistor comprising a source, adrain, and a carbon nanotube bridge between the source and the drain,the carbon nanotube bridge being formed by carbon nanotubes grown in ahorizontal direction between the source and the drain, so that the fieldeffect transistor can control a flow of electrons.

[0027] In this case, the carbon nanotube bridge formed between thesource and the drain comprises carbon nanotubes having a characteristicof semiconductor.

[0028] Moreover, on the carbon nanotube bridge formed between the sourceand the drain, a plurality of gate carbon nanotubes are formedintersecting the carbon nanotube bridge between the source and the drainat, so as to produce an energy barrier to form a quantum point and tocontrol the flow of the electric current.

[0029] Also, the quantum point has a size, which is controlled by usinga common terminal, when the gate carbon nanotube bridges form gates.

[0030] Furthermore, the field effect transistor also comprises first andsecond wires, through which electric current can pass, and which areprovided on the source and the drain, so as to magnetize catalysts beingin contact with the source and the drain in a desired direction. Thefirst wire disposed on the source and the second wire disposed on thedrain are arranged in parallel with each other.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The above objects, and other features and advantages of thepresent invention will become more apparent after a reading of thefollowing detailed description when taken in conjunction with thedrawings, in which.

[0032]FIG. 1 is a view for schematically showing a conventional methodof vertically growing carbon nanotubes;

[0033]FIG. 2 a view for schematically showing another conventionalmethod of horizontally growing carbon nanotubes, which has beendisclosed by Hong Jie Die;

[0034]FIGS. 3A to 3D are views for showing a method of horizontallygrowing carbon nanotubes according to one embodiment of the presentinvention;

[0035]FIG. 4 is a perspective view of an object fabricated by the methodshown in FIGS. 3A to 3D;

[0036]FIG. 5A or FIG. 5B are sectional views, which respectively show ahole type, in which apertures extend through a vertical growthpreventing layer and a first substrate, and a well type, in which aportion of the first substrate is not etched but remains so that each ofthe apertures does not extend entirely through the vertical growthpreventing layer and the first substrate;

[0037]FIGS. 6A to 11 are views for showing various shapes of carbonnanotubes, which have been horizontally grown by the method ofhorizontally growing carbon nanotubes according to the presentinvention;

[0038]FIGS. 12A and 12B are views for showing constructions, in which ametal is patterned to make a junction or junctions with the carbonnanotubes horizontally grown by the method of horizontally growingcarbon nanotubes according to the present invention;

[0039]FIGS. 13A to 13D are views for schematically showing anothermethod of horizontally growing carbon nanotubes according to anotherembodiment of the present invention;

[0040]FIGS. 14A to 14C are views for schematically showing anothermethod of horizontally growing carbon nanotubes according to anotherembodiment of the present invention;

[0041]FIGS. 15A to 15C are views for schematically showing a process ofhorizontally growing the carbon nanotubes at desired locations by themethod of horizontally growing the carbon nanotubes according to thepresent invention;

[0042]FIGS. 16A to 17D are views for showing a method of selectivelygrowing carbon nanotubes in a horizontal direction, in which thecatalyst metal is formed in a shape of nanowires and the location forforming the catalyst can be controlled by wet etching;

[0043]FIGS. 18A and 18B are views for schematically showing the processof nano imprint lithography for forming nanodots or nanowires in themethod of horizontally growing carbon nanotubes according to the presentinvention;

[0044]FIG. 19 is a view for schematically showing the self-assemblymethod for forming the nanodots or nanowires in the method ofhorizontally growing carbon nanotubes according to the presentinvention;

[0045]FIG. 20 is a view for schematically showing the construction of aspin valve single electron transistor utilizing the carbon nanotubesaccording to the present invention;

[0046]FIG. 21 is a perspective view of the spin valve single electrontransistor according to the present invention as shown in FIG. 20;

[0047]FIG. 22 is a view for schematically showing a spin valve singleelectron transistor according to another embodiment of the presentinvention; and

[0048] FIGS. 23 to 26 are views for schematically showing various fieldeffect transistors formed by the method of horizontally growing carbonnanotubes according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0049] The above and other objects, characteristics, and advantages ofthe present intention will be apparent from the following descriptionalong with the accompanying drawings.

[0050]FIGS. 3A to 3D are views for showing a method of horizontallygrowing carbon nanotubes according to one embodiment of the presentinvention, and FIG. 4 is a perspective view of an object fabricated bythe method shown in FIGS. 3A to 3D.

[0051] Referring to FIGS. 3A to 4, the method of horizontally growingcarbon nanotubes according to the present invention includes the stepsof: (a) forming a predetermined catalyst pattern 12 on a first substrate10; (b) forming a vertical growth preventing layer 14 on the firstsubstrate 10, which prevents carbon nanotubes from growing in a verticaldirection; (c) forming apertures 16 through the vertical growthpreventing layer 14 and the first substrate 10 to expose the catalystpattern 12 through the apertures 16; and (d) synthesizing carbonnanotubes at exposed surfaces 18 of the catalyst pattern 12, so as togrow the carbon nanotubes in the horizontal direction.

[0052] Various materials such as silicon, glass, silicon oxide, glasscoated with indium tin oxide (ITO) may be employed as the firstsubstrate 10 and the vertical growth preventing layer 14 depending onobjects.

[0053] As for the above-mentioned catalyst, all kinds of materials, atwhich the carbon nanotubes can grow, including metal, metal alloy,superconducting metal, and other special metal, may be utilized. Also,those materials may be formed to be the predetermined pattern 12 by suchprocesses as lithography, sputtering, and evaporation.

[0054] In this case, the apertures 16 located at specific positions ofthe catalyst pattern may be formed by such methods as laser drilling,wet etching, and dry etching. Meanwhile, in a more detailed description,the apertures 16 may be a hole type, in which the apertures 16 extendthrough the vertical growth preventing layer 14 and the first substrate10 as shown in FIG. 5A, or a well type, in which a portion of the firstsubstrate 10 is not etched but remains so that each of, the apertures 16does not extend entirely through the vertical growth preventing layer 14and the first substrate 10 as shown in FIG. 5B.

[0055] Then, the object as shown in FIG. 5A or FIG. 5B, which isprepared through the above process, is put in an apparatus forsynthesizing carbon nanotubes and is synthesized, so that each carbonnanotube grows only at the exposed surfaces 18 of the catalyst pattern,which is exposed to a source gas. That is, the carbon nanotubes growonly in a horizontal direction, which is parallel to the first substrate10.

[0056] In this case, such methods as a catalyst thermal decompositionmethod, a plasma vapor deposition method, and a hot-filament vapordeposition method can be utilized in synthesizing the carbon nanotubes.Further, a compound of hydrocarbon such as methane, acetylene, carbonmonoxide, benzene, and ethylene can be used as a raw material

[0057] In the meantime, FIGS. 6A, 6B and 11 illustrate various shapes ofcarbon nanotubes, which are horizontally grown by the method ofhorizontally growing carbon nanotubes according to the presentinvention.

[0058]FIGS. 6A and 6B show a carbon nanotube 20, which is grown at astraight-line-type catalyst pattern 12, and in which the aperture isformed at a predetermined portion of the catalyst pattern. In this case,by properly controlling the synthesizing time, optionally obtained canbe a carbon nanotube 20 of a bridge construction, in which the exposedsurfaces 18 of the catalyst pattern opposed to each other are connectedwith each other through the carbon nanotube, or a carbon nanotube of afree-hang construction, in which the opposed exposed surfaces 18 are notconnected with each other.

[0059] In the meantime, the diameter of the grown carbon nanotube 20 canbe determined by controlling the area or the size of the particles ofthe exposed catalyst surface, and the exposed catalyst surface can havevarious surface states by changing the condition of forming the patternor through a subsequent treatment such as a plasma treatment and an acidtreatment. Therefore, through the process as described above, at leasttwo carbon nanotubes 20 may be grown at a single exposed surface, andthe carbon nanotubes 20 grown at the opposed exposed surfaces 18 of thecatalyst pattern may have different constructions, that is, differentdiameters, different chiralitys, etc., as shown in FIG. 6B.

[0060]FIGS. 7A to 7D respectively show a carbon nanotube horizontallygrown on an intersection-type catalyst pattern, in which the aperturesare formed on the intersection area of the catalyst pattern.

[0061] Likewise in the straight-line-type catalyst pattern, a carbonnanotube 20 of the bridge construction as shown in FIG. 7A or a carbonnanotube 20 of the free-hang construction as shown in FIG. 7C may beobtained also in this intersection-type catalyst pattern. Further, thecarbon nanotubes 20 grown at the exposed surfaces of the catalystpattern opposed to each other may have different diameters from eachother as shown in FIG. 7C, and at least two carbon nanotubes 20 may hegrown at one exposed surface as shown in FIG. 7B. Also, by growing aplurality of carbon nanotubes at each of the exposed surfaces ofcatalyst pattern, the grown carbon nanotubes may have a mesh shape asshown in FIG. 7D.

[0062] Moreover, as shown in FIG. 7A, by controlling the height of thecatalyst pattern in the vertical direction and in the horizontaldirection, carbon nanotubes 20 can be grown while intersecting with eachother, and this can be utilized as a gate element. Further, the carbonnanotubes grown while intersecting with each other may be in mechanicalcontact with each other, so as to form an electric junction, which canbe directly utilized in the junction analysis, and this junctioncharacteristic may be utilized by elements.

[0063] In this case, as a method for facilitating the formation of thejunction, thermal expansion/contraction of material may be utilized.Since the synthesis of the carbon nanotubes is usually carried out at atemperature between 500° C. and 900° C., the contact between the carbonnanotubes 20 grown intersecting can be facilitated by utilizing aphenomenon of the thermal contraction, which happens in a cooling stageafter the synthesis.

[0064]FIGS. 8, 9, 10, and 11 respectively show a carbon nanotubehorizontally grown at a radial catalyst pattern, a circular catalystpattern, a rectangular catalyst pattern, and a construction having atleast two grooves arranged on at least two catalyst patterns ofstraight-line-type, respectively in which the apertures are formed atintersecting areas, an interior of the circle, and an interior of therectangle of the pattern.

[0065]FIGS. 6A to 11 show various shapes of the carbon nanotubeshorizontally grown according to the present invention, which does notlimit the scope of the invention but the catalyst pattern may bemodified in a more efficient way in being applied to the nano-devices.

[0066] Meanwhile, FIGS. 12A and 12B show constructions, in which a metal20 is patterned to make a junction or junctions with the carbonnanotubes 20 horizontally grown by the method of horizontally growingcarbon nanotubes according to the present invention. Consequently, thejunction between the carbon nanotubes 20 and the metal 30 can be easilyachieved, and such junction can be optionally formed at a specificlocation.

[0067] Further, by utilizing the above-mentioned method, a carbonnanotube/carbon nanotube junction, a carbon nanotube/metal junction, anda carbon nanotube/semiconductor junction can be optionally formed atdesired locations.

[0068] Meanwhile, FIGS. 13A to 13D are views for schematically showinganother method of horizontally growing carbon nanotubes according toanother embodiment of the present invention.

[0069] Referring to FIGS. 13A to 13D, the method of horizontally growingcarbon nanotubes according to another embodiment of the presentinvention includes the steps of: (i) forming masks 40 at predeterminedlocations on a first substrate 10; (j) forming the catalyst pattern 12on the first substrate 10 and the masks 40 formed on the first substrate10; (k) forming a vertical growth preventing layer 14 on the firstsubstrate 10, which prevents carbon nanotubes from growing in a verticaldirection; (l) eliminating the masks 40 from the vertical growthpreventing layer 14 and the first substrate 10, so as to form apertures42 and expose the catalyst pattern 12; and (m) synthesizing carbonnanotubes at the exposed locations of the catalyst pattern, so as togrow the carbon nanotubes in the horizontal direction.

[0070] In the present embodiment, the material of the first substrate 10and the catalyst pattern 12, the method of forming the catalyst pattern,and the method of synthesizing the carbon nanotubes are the same asthose in the first embodiment. Further, the masks 40, which can beeasily eliminated by etching, heating, etc., are formed on the substrateby such a method as evaporation. Further, the catalyst pattern may beformed in various shapes including a straight-line shape, anintersection shape, a radial shape, a circular shape, and a rectangularshape. Also by the present embodiment, the carbon nanotubes grown in thehorizontal direction as shown in FIGS. 6A to 11 can be obtained.

[0071]FIGS. 14A to 14C are views for schematically showing anothermethod of horizontally growing carbon nanotubes according to anotherembodiment of the present invention.

[0072] Referring to FIGS. 14A to 14C, the method of horizontally growingcarbon nanotubes according to the present embodiment of the inventionincludes the steps of: forming a catalyst pattern 12 in a predeterminedtwo-dimensional arrangement on the first substrate 10; fabricating aseparate substrate 50 for preventing vertical growth of the carbonnanotubes having holes 52 in a predetermined arrangement; placing thevertical growth preventing substrate 50 over the first substrate 10having the catalyst pattern 12 with a predetermined gap 54; andsynthesizing the carbon nanotubes at the catalyst pattern 12 so as tohorizontally grow the carbon nanotubes.

[0073] In this case, the kinds of the first substrate 10 and thecatalyst pattern 12, the method of forming the catalyst pattern, and themethod of synthesizing the carbon nanotubes in the present embodimentare the same as those in the first embodiment. Further, the holes 52 ofthe second substrate 50 for preventing vertical growth of the carbonnanotubes may be formed by such methods as laser drilling, wet etching,and dry etching. In the step of placing the vertical growth preventingsubstrate 50 over the first substrate 10, a space in which the carbonnanotubes can grow will do for the predetermined gap 54 between the twosubstrates 10 and 50, and spacers 56 can be disposed between the cornersof the first and the second substrates 10 and 50, so as to maintain thegap therebetween.

[0074] Meanwhile, FIGS. 15A to 15C are schematic views for showing aprocess of horizontally growing the carbon nanotubes at desiredlocations by means of a catalyst having a shape of nanodots ornanowires, in the method of horizontally growing the carbon nanotubesaccording to the present invention.

[0075] First, referring to FIG. 15A, catalyst metal patterned in a shapeof nanodots or nanowires is deposited on a silicon substrate having anoxide film formed thereon. In this case, the same material as thecatalyst pattern 12 as described above is usually used as the catalystmetal.

[0076] Further, as shown in FIG. 15B, such material as Palladium (Pd),Niobium (Nb), Molybdenum (Mo), or an insulator of silicon nitride (SiN)film or silicon oxide (SiO₂) film is deposited to form a growthpreventing layer on the nanodots or the nanowires. This layer functionsto prevent the carbon nanotubes from growing in the vertical directionfrom the catalyst, and further functions as an electrode in the case ofthe metal. In this case, the growth preventing layer can be patterned ina desired shape by such a general semiconductor process as a photoresist process (PR process) and a lithography process.

[0077] Accordingly, as shown in FIG. 15C, on the substrate having agrowth preventing layer formed in a pattern, the carbon nanotubes can begrown in the horizontal direction from the catalyst by means of achemical vapor deposition method.

[0078]FIGS. 16A to 17D are views for showing a method of selectivelygrowing carbon nanotubes in a horizontal direction, in which thecatalyst metal is formed in a shape of nanowires and the location forforming the catalyst can be controlled by wet etching.

[0079] First, as shown in FIGS. 16A and 17A, catalyst metal patterned ina shape of nanowires is deposited on a silicon substrate having an oxidefilm formed thereon. In this case, the same material as the catalystpattern 12 as described above is usually used as the catalyst metal.

[0080] Further, as shown in FIGS. 16B and 17B, such material asPalladium (Pd), Niobium (Nb) Molybdenum (Mo), or an insulator of siliconnitride (SiN) film or silicon oxide (SiO₂) film is deposited to form agrowth preventing layer on the catalyst in the shape of the nanodots orthe nanowires with a predetermined gap therebetween. This layerfunctions to prevent the carbon nanotubes from growing in the verticaldirection from the catalyst, and further functions as an electrode inthe case of the metal.

[0081] The growth preventing layer can be patterned in a desired shapeby such a general semiconductor process as a photo resist process and alithography process. In this case, FIG. 17B shows the case, in which anerror happens in the course of forming the pattern, that is, the case,in which the catalyst is exposed at an undesired area in the course ofpatterning the growth preventing layer.

[0082] Moreover, as shown in FIGS. 16C and 17C, the catalyst having theshape of nanowires in an area, in which the growth preventing layer isnot formed, that is, the catalyst in an undesired area, is eliminated bymeans of wet etching. In this case, in the case of carrying out the wetetching, since an isotropic etching is carried out, the catalyst metalis further etched inward of the growth preventing layer (see FIG. 16C),so that the function of the growth preventing layer, which means toprevent the carbon nanotubes from growing in the vertical direction,becomes more important.

[0083] Further, in the case where the catalyst is formed in the shape ofnanowires, even when an excessive etching has been carried out, thecatalyst, from which the carbon nanotubes can be grown, remains on thesubstrate, so as to form a more efficient growth preventing layer,differently from the case of the catalyst in the shape of the nanodots.Further, as shown in FIGS. 17B and 17C, even when the pattern of thegrowth preventing layer is erroneously formed in the lithographyprocess, the error generated in the lithography process can be settledby means of the wet etching.

[0084] Therefore, by means of the chemical vapor deposition method, thecarbon nanotubes can be horizontally grown between the catalysts formedunder the growth preventing layer spaced therefrom with a predeterminedgap.

[0085] Meanwhile, in the embodiments shown in FIGS. 15A to 17D, thefollowing methods already known in public may be utilized as the methodof forming the catalyst pattern on the substrate in the shape ofnanodots or nanowires.

[0086] One of those methods is to utilize the process of nano imprintlithography as shown in FIGS. 18A and 18B. FIGS. 18A and 18B are viewsfor schematically showing the process of nano imprint lithography forforming nanodots or nanowires in the method of horizontally growingcarbon nanotubes according to the present invention.

[0087] The nano imprint lithography is an imprinting process, in which astamp having a nano-pattern is pressed onto a high-molecular thin film,to form a high-molecular pattern in a size of nanometers, which can beapplied to a large area wafer, as shown in FIGS. 18A and 18B. The nanoimprint lithography is a process for simply fabricating a pattern havinga size of several tens nanometers, which is largely simplified incomparison with a process of forming the large area nanopattern by meansof the existing fine optical processing technology.

[0088] Further, the catalyst pattern of nanodots or nanowires can beformed by means of a self-assembly method as shown in FIG. 19, which isa view for schematically showing the self-assembly method for formingthe nanodots or nanowires in the method of horizontally growing carbonnanotubes according to the present invention.

[0089] In the self-assembly method as mentioned above, the upper surfaceof the substrate made from such metal as gold Au or silicon Si is coatedwith such a specific material capable of being adsorbed to the surfaceas surface-active headgroup, which are mostly organic molecules adsorbedin a mono-molecule layer, and then is coated with a material in alkylgroup, which enables a connection to a material to be coated thereon.Thereafter, a material of surface group having the characteristic offilm is coated thereon, so that an ultra fine thin film having variouslayers from a single layer to a plurality of layers can be fabricated.

[0090] That is, the specific material capable of being adsorbed to thesubstrate is applied, and a material functioning as a bridge to thematerial of thin film to be deposited are applied and then the desiredmaterial of thin film is deposited. After the specific material capableof performing chemical adsorption is deposited on the surface, and thenit is patterned by means of scanning tunneling microscope/atomic forcemicroscope (STM/AFM), so that an ultra fine thin film having a desiredpattern can be obtained.

[0091] In the meantime, FIG. 20 is a view for schematically showing theconstruction of a spin valve single electron transistor utilizing thecarbon nanotubes according to the present invention, and FIG. 21 is aperspective view of the spin valve single electron transistor accordingto the present invention as shown in FIG. 20. The spin valve singleelectron transistor as follows can be obtained by utilizing the carbonnanotubes grown in the horizontal direction of the substrate by themethod of horizontally growing carbon nanotubes as described above.

[0092] Referring to FIGS. 20 and 21, in the spin valve single electrontransistor according to the present invention, the carbon nanotubes aregrown in the horizontal direction between a source 210 and a drain 220to form a carbon nanotube bridge 260, which enables the flow of theelectric current by the unit of electron to be controlled In this case,the carbon nanotube bridge 260 formed between the source 210 and thedrain 220 consists of carbon nanotubes having the characteristic ofsemiconductor.

[0093] Further, the carbon nanotube bridge 260 formed between the source210 and the drain 220 is formed on a plurality of gate carbon nanotubes270 and 280, which are formed in such a manner as to produce an energybarrier to form a quantum point and to control the flow of the electriccurrent.

[0094] Further, wires 251 and 252, through which electric current canpass, are provided on the source 210 and the drain 220, so as tomagnetize the catalyst being in contact with the source 210 and thedrain 220 in a desired direction. Furthermore, the source wire 251disposed on the source 210 and the drain wire 252 disposed on the drain220 are arranged in parallel to each other.

[0095] Meanwhile, FIG. 22 is a view for schematically showing a spinvalve single electron transistor according to another embodiment of thepresent invention.

[0096] Referring to FIG. 22, when a plurality of gate carbon nanotubebridges 470 and 480 form gates 430 and 440, the size of the quantumpoint is controlled by using a common terminal 490. Other elements inthe present embodiment are the same as those described with reference toFIGS. 20 and 21.

[0097] Hereinafter, the description will be on an operation of the spinvalve single electron transistor utilizing carbon nanotubes according tothe present invention, which has the construction as described above.

[0098] Referring to FIGS. 20 and 21, in the carbon nanotube bridge 260of the semiconductor characteristic formed between the source 210 andthe drain 220, a positive voltage is applied to the carbon nanotubebridges 270 and 280, which are respectively defined as first and secondgates 230 and 240. Consequently, the electric charges may beinsufficient in the points C1 and C2, which results in a formation ofenergy barriers at the points C1 and C2. In this case, in the case ofthe carbon nanotube bridge 260 between the source 210 and the drain 220,the portion between the points C1 and C2 is isolated from thesurrounding forming the quantum point.

[0099] Further, since the electrodes of the source 210 and the drain 220are in contact with the carbon nanotube bridge 260 through thetransition metal catalyst, the catalyst being in contact with the source210 and the drain 220 can be magnetized in a desired direction bytransmitting electric currents defined as I_(m1) and I_(m2) inconsideration of a proper coercive force.

[0100] By the method as described above, the spin of the electroninjected into the source 210 can be controlled. In this case, the spinof the injected electron can be conserved when portions of the carbonnanotube bridge 260 between the source 210 and the point C1 and betweenthe point C2 and the drain 220 are ballistic conductors.

[0101] Therefore, in the case where an electron makes an access bytunneling to the quantum point formed between the points C1 and C2, thetunneling is easily generated when the spin directions are the samewhile it is not easily generated when the spin directions are differentfrom each other, according to the magnetized direction of the source 210and the drain 220.

[0102] As described above, the spin-related single electron transistorcan be obtained by controlling the electric current transmitting throughthe carbon nanotube bridge 260 for channels.

[0103] In the meantime, FIGS. 23 to 26 are views for schematicallyshowing various field effect transistors formed by the method ofhorizontally growing carbon nanotubes according to the presentinvention. Referring to FIGS. 23 to 26, various constructions of thefield effect transistors will be described hereinafter.

[0104]FIG. 23 shows a field effect transistor, in which gates aredisposed at both sides of the carbon nanotube. In this example, suchmetal as Niobium (Nb), Molybdenum (Mo) can be used as an electrode or anelectrode layer for the growth preventing film. Further, a catalystlayer used as the catalyst is disposed under the electrode layers ofsource and drain. In this case, the same material as the catalystpattern 12 described above can be used as the catalyst, and suchmaterials as nickel (Ni), iron (Fe), and cobalt (Co) are usually used.

[0105] In this case, the gate electrodes are disposed at both sides ofthe source and the drain. Moreover, the carbon nanotube is synthesizedbetween the gate electrodes by means of thermal chemical vapordeposition method (TCVD). Therefore, a geometrical design including thespace between the gate electrodes is required, so that the carbonnanotube can be synthesized between the gate electrodes. In this case,it is preferred that the space between the gates is designed to have anelongated construction, that is, a long and narrow construction, so thatthe growth of the carbon nanotube is controlled while the electric fieldby the gates is sufficiently generated.

[0106]FIG. 24 shows a field effect transistor, in which the gateconstruction is located at the bottom. In this example, under thecatalyst layer is disposed a buffer layer for facilitating a heightadjustment and an adhesion to an insulating layer of a wafer, since theheight of the catalyst layer has to be larger than that of the gate.

[0107] Further, the carbon nanotube may be warped by the electric field,since it has a good elasticity. In this case, the degree of the warpchanges according to the kind and the length of the carbon nanotube.Although the maximum degree of the warp may be several tens nanometers,it is anticipated that the carbon nanotube is generally warped byseveral nanometers. Therefore, the construction shown in FIG. 23 isdesigned in such a manner as that the distance between the gates islarger than the width of the catalyst, on which the carbon nanotube isgrown, by more than several tens nanometers. In the case of the groundgate shown in FIG. 24, a thin dielectric layer may be deposited on thegate electrode according to necessity. Meanwhile, FIG. 25 shows aconstruction, in which the carbon nanotubes are used as the gates.

[0108] In the meantime, when the carbon nanotube is synthesized, thecarbon nanotube may grow vertically to the surface of the electrode, andit is very difficult to grow the carbon nanotube from the desiredposition to the opposed catalyst layer while the carbon nanotube has thesemiconductor characteristic. In order to settle these problems, a pathfor functioning as a guide to lead the growth of the carbon nanotube,that is, a passage for the growth of the carbon nanotube, may bearranged between the catalyst layers, and the carbon nanotube may begrown in the path or the passage (see FIG. 26).

[0109] In this case, the guide for the growth of the carbon nanotube canbe very precisely fabricated on the silicon oxide film by such a dryetching as a reactive ion etching (RIE). Then, catalyst is deposited onboth ends of the guide, and then an electrode is deposited thereon.Also, the gates are disposed beside the guide. Rather, the gates may belocated on the surface of the dielectric as shown in the drawing, andthe gate electrodes may he placed on etched areas like the catalystlayers, so that the gate electrodes can apply electric field at the sameheight as that of the catalyst layer or the carbon nanotube.

[0110] The constructions shown in FIGS. 23 and 24 can be fabricatedthrough two times of lithography processes. However, the constructionsshown in FIGS. 25 and 26 require three times of lithography processes.In this case, the construction shown in FIG. 25 can be fabricated notonly as the field effect transistor (PET) but also as a tunnelingtransistor. Moreover, in the case where at least two carbon nanotubesare disposed as the gates, fabricated can be the Kondo element utilizingthe Kondo resonance or the single electron transistor (SET) according tothe gate-bias. In the construction shown in FIG. 26, the carbon nanotubeis prevented from growing in an undesired direction when synthesized, sothat the defect is reduced.

[0111] While there have been illustrated and described what areconsidered to be preferred specific embodiments of the presentinvention, it will be understood by those skilled in the art that thepresent invention is not limited to the specific embodiments thereof,and various changes and modifications and equivalents may be substitutedfor elements thereof without departing from the true scope of thepresent invention.

What is claim is:
 1. A method of horizontally growing carbon nanotubes,the method comprising the steps of: (a) forming a predetermined catalystpattern on a first substrate; (b) forming a vertical growth preventinglayer on the first substrate, which prevents carbon nanotubes fromgrowing in a vertical direction; (c) forming apertures through thevertical growth preventing layer and the first substrate to expose thecatalyst pattern through the apertures; and (d) synthesizing carbonnanotubes at exposed surfaces of the catalyst pattern in order to growthe carbon nanotubes in the horizontal direction.
 2. A method as claimedin claim 1, wherein the apertures formed in step c are of a hole-type,in which the apertures extend entirely through the vertical growthpreventing layer and the first substrate.
 3. A method as claimed inclaim 1, wherein the apertures formed in step c are of a well-type, inwhich the first substrate is partially etched, so that the aperturesextend through the vertical growth preventing layer and a portion of thefirst substrate.
 4. A method as claimed in claim 1, wherein the catalystpattern has one of a straight-line shape, an intersection shape, aradial shape, a circular shape, and a rectangular shape, while theapertures are formed at intersecting areas of the catalyst pattern of astraight line shape, an intersection shape, and a radial shape, at aninterior of a circle, and at an interior of a rectangle of the pattern.5. A method as claimed in claim 4, wherein the carbon nanotubes formedrespectively from the catalyst pattern and the apertures are grown tomake a junction between them.
 6. A method as claimed in claim 5, whereinthe junction between the carbon nanotubes intersecting each other isformed by means of a phenomenon of thermal contraction of material,which is generated in a cooling stage after the carbon nanotubes aregrown.
 7. A method as claimed in claim 4, wherein the carbon nanotubesformed from the catalyst pattern and the apertures, respectively, aregrown while intersecting each other.
 8. A method as claimed in claim 1,wherein the carbon nanotubes grown in step d forms a bridgeconstruction, by which exposed surfaces of the catalyst pattern opposingeach other are connected with each other.
 9. A method as claimed inclaim 1, wherein the carbon nanotubes grown in step d forms a free-hangconstruction, in which the carbon nanotubes from the exposed surfaces ofthe catalyst pattern opposing each other are separated from each other.10. A method as claimed in claim 1, wherein the carbon nanotubes grownin step d are a plurality of carbon nanotubes grown at a single catalystpattern.
 11. A method as claimed in claim 1, wherein the carbonnanotubes grown in step d forms a mesh construction, in which aplurality of carbon nanotubes are grown from each of the exposedsurfaces of catalyst pattern opposing each other, to be connected witheach other.
 12. A method as claimed in claim 1, the method furthercomprising a step of patterning a metal on a grown carbon nanotubes, soas to selectively form a junction between the carbon nanotube and themetal at a specific location, after step d.
 13. A method of horizontallygrowing carbon nanotubes, the method comprising the steps of: (i)forming masks at predetermined locations on a first substrates (j)forming a catalyst pattern on the first substrate and the masks formedon the first substrate; (k) forming a vertical growth preventing layeron the first substrate, which prevents the carbon nanotubes from growingin a vertical direction; (l) eliminating the masks from the verticalgrowth preventing layer and the first substrate to form apertures andexpose the catalyst pattern; and (m) synthesizing the carbon nanotubesat exposed locations of the catalyst pattern in order to grow the carbonnanotubes in the horizontal direction.
 14. A method as claimed in claim13, wherein the catalyst pattern has one of a straight line shape, anintersection shape, a radial shape, a circular shape, and a rectangularshape, while the apertures are formed at intersecting areas of thecatalyst pattern of a straight line shape, an intersection shape, and aradial shape, at an interior of a circle, and at an interior of arectangle of the pattern.
 15. A method as claimed in claim 14, whereinthe carbon nanotubes formed respectively from the catalyst pattern andthe apertures are grown to make a junction between them.
 16. A method asclaimed in claim 14, wherein the carbon nanotubes formed respectivelyfrom the catalyst pattern and the apertures are grown while intersectingeach other.
 17. A method as claimed in claim 13, wherein the carbonnanotubes grown in step m forms a bridge construction, by which exposedsurfaces of the catalyst pattern opposing each other are connected witheach other.
 18. A method as claimed in claim 1, wherein the carbonnanotubes grown in step m forms a free-hang construction, in which thecarbon nanotubes from the exposed surfaces of the catalyst patternopposing each other are separated from each other.
 19. A method asclaimed in claim 13, the method further comprising a step of patterninga metal on a grown carbon nanotubes in order to selectively form ajunction between the carbon nanotube and the metal at a specificlocation, after step m.
 20. A method of horizontally growing carbonnanotubes, the method comprising the steps of: forming a catalystpattern in a predetermined two-dimensional arrangement on a firstsubstrate; fabricating a second substrate for preventing vertical growthof the carbon nanotubes having holes in a predetermined arrangement;placing the second substrate for preventing vertical growth of thecarbon nanotubes over the first substrate having the catalyst patternwith a predetermined gap; and synthesizing the carbon nanotubes at thecatalyst pattern, so as to horizontally grow the carbon nanotubes.
 21. Amethod of horizontally growing carbon nanotubes, the method comprisingthe steps of: forming a catalyst in a shape of nanodots or nanowires ona substrate; patterning a growth preventing layer on the catalyst in theshape of nanodots or nanowires, so as to prevent the nanodots ornanowires from growing in a vertical direction; and selectively growingthe carbon nanotubes in a horizontal direction at the nanodots ornanowires.
 22. A method as claimed in claim 21, wherein the catalyst inthe shape of the nanodots or nanowires are patterned by an imprintmethod.
 23. A method as claimed in claim 21, wherein the catalyst in theshape of the nanodots or nanowires are patterned by a self-assemblymethod.
 24. A method as claimed in claim 21, wherein the growthpreventing layer is formed of an insulator film made from a compoundselected from the group consists of silicon nitride (SiN) and siliconoxide (SiO₂).
 25. A method as claimed in claim 21, wherein the growthpreventing layer is formed from a metal selected from the group consistsof Palladium (Pd), Niobium (Nb), and Molybdenum (Mo).
 26. A method ofhorizontally growing carbon nanotubes, the method comprising the stepsof: forming catalysts in a shape of nanowires an a substrate; forming agrowth preventing layer on the catalysts having the shape of nanowiresby a semiconductor process including a lithography process, the growthpreventing layer being spaced from the substrate with a, predeterminedgap; eliminating a portion of the catalysts having the shape ofnanowires in an area at which the growth preventing layer is not formed,by means of a wet etching; and growing the carbon nanotubes in ahorizontal direction between the catalysts formed under the growthpreventing layer spaced from the substrate with a predetermined gap, bymeans of a chemical vapor deposition method.
 27. A method as claimed inclaim 26, wherein the catalyst in the shape of nanowires are patternedby an imprint method.
 28. A method as claimed in claim 26, wherein thecatalyst in the shape of nanowires are patterned by a self-assemblymethod.
 29. A field effect transistor comprising a source, a drain, anda carbon nanotube bridge between the source and the drain, the carbonnanotube bridge being formed by carbon nanotubes grown in a horizontaldirection between the source and the drain, so that the field effecttransistor can control the flow of electrons.
 30. A field effecttransistor as claimed in claim 29, wherein the carbon nanotube bridgeformed between the source and the drain comprises carbon nanotubeshaving a characteristic of semiconductor.
 31. A field effect transistoras claimed in claim 29, wherein, on the carbon nanotube bridge formedbetween the source and the drain, a plurality of gate carbon nanotubesare formed intersecting the carbon nanotube bridge between the sourceand the drain at, so as to produce an energy barrier to form a quantumpoint and to control the flow of the electric current.
 32. A fieldeffect transistor as claimed in claim 31, wherein the quantum point hasa size, which is controlled by using a common terminal, when the gatecarbon nanotube bridges form gates.
 33. A field effect transistor asclaimed in claim 29, the field effect transistor further comprisingfirst and second wires, through which electric current can pass, andwhich are provided on the source and the drain, so as to magnetizecatalysts being in contact with the source and the drain in a desireddirection.
 34. A field effect transistor as claimed in claim 33, whereinthe first wire disposed on the source and the second wire disposed onthe drain are arranged in parallel with each other.
 35. A field effecttransistor as claimed in claim 29, wherein a guide groove is formed at asubstrate of the field effect transistor to allow the carbon nanotubesto be grown in a horizontal direction between the source and the drain,thereby the carbon nanotube bridge is formed in the horizontal directionbetween the source and the drain.